DISSERTATION RESEARCH: Origins of alternate ecosystem states - effects of drought on postfire tree regeneration and shifting dominance of western conifers

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This doctoral dissertation research seeks to understand how drought following wildfires affects the establishment of two widespread Rocky Mountain tree species, lodgepole pine and Douglas-fir. In Yellowstone National Park, warming, drying conditions are leading to increased frequency of severe wildfires that kill existing trees and trigger regrowth of the forest. These trends are expected to continue. Many tree species in Yellowstone are well adapted to fire. Yet, early and abundant seedling establishment after fire is critical for forests to recover. Tree seedlings are particularly sensitive to drought, and evidence suggests that sufficiently dry postfire conditions could cause the widespread death of tree-seedlings, with consequences that may last decades. This research will determine how seedlings from two tree species respond to drought conditions expected in the mid-21st century and will identify the mechanisms that influence seedling response to dry conditions. The results of this study will advance understanding of how forests in the western United States will respond to environmental change over the coming decades and provide useful information for western land managers who are grappling with increased wildfires. In addition to providing important scientific knowledge, the study will provide opportunities for undergraduate students to experience research in the field of forest ecology. Researchers will also engage local residents of the Greater Yellowstone area by presenting an exhibit of science art in local shops that features photographs of the research. A handout will accompany the exhibit that presents the study findings to residents, such as how changing forests may influence recreational opportunities.This research will address the questions: How will 21st century drought alter postfire regeneration of a widespread western conifer? Will future climate conditions favor an alternate dominant tree species of non-forest cover? A greenhouse experiment will be conducted, where a combination of projected growing season daily temperature and soil-moisture conditions will be simulated to determine how expected drought will influence rates of postfire tree-seedling establishment in different soil types. The experiment will be conducted in a unique facility at the University of Wisconsin-Madison in which environmental conditions can be controlled at sub-daily resolutions, and the work will complement an ongoing field-based experiment in Yellowstone. Results will be integrated into process-based models to explore consequences of drought and increased fire activity at landscape and regional scales.